


A Covenant of Souls

by shirasade



Category: Shadowhunters (TV)
Genre: Alternate Universe - Merpeople, Drowning, First Meetings, M/M, Making Out, POV Jace Wayland, Parabatai Bond, Weird Biology
Language: English
Status: Completed
Published: 2020-12-24
Updated: 2020-12-24
Packaged: 2021-03-11 04:55:48
Rating: Mature
Warnings: No Archive Warnings Apply
Chapters: 1
Words: 4,725
Publisher: archiveofourown.org
Story URL: https://archiveofourown.org/works/28269489
Author URL: https://archiveofourown.org/users/shirasade/pseuds/shirasade
Summary: When Jace opened his eyes again, even before taking in his surroundings, he noticed with great surprise that he was breathing. Then he realized that he was still in the water.Underthe water, to be precise.
Relationships: Alec Lightwood/Jace Wayland
Comments: 7
Kudos: 38
Collections: Hunter's Moon Fic Recs, Jalec Secret Santa 2020, Shirasade's Shadowhunters AUs





	A Covenant of Souls

**Author's Note:**

  * For [Jessa](https://archiveofourown.org/users/Jessa/gifts).



> For the Jalec Secret Santa, for Jessa. Prompt: Hurt/comfort (emotional or physical) angst, fluff and angst, canonverse or AU, NSFW or SFW. I have a kink for wings or mer AU would be fun but is not essential. I love first kisses or first confessions of feelings / first love confessions. Parabatai bond, rune healing.
> 
> I hope you like this, hun, as I've been struggling with writing block pretty much all through this benighted year! <3
> 
> Title is a play of the famous verse about David and Jonathan making their covenant:  
>  _And it came to pass [...] that the soul of Jonathan was knit with the soul of David, and Jonathan loved him as his own soul. [...] Then Jonathan and David made a covenant, because he loved him as his own soul._ (1 Samuel 18: 1-3)

Jace was pretty sure he was dying. The men who'd killed his father had chased him to a cliff, and with night falling he'd lost his footing and had plummeted straight into the icy waves of the sea below. Miraculously he hadn't hit any rocks, but maybe unconsciousness would have been preferable to the panicky struggle for breath and useless flailing of limbs that got ever more sluggish.

He felt almost resigned to it. He was 16 years old, and he was going to die without a single person to mourn him.

***

When he opened his eyes again, even before taking in his surroundings, he noticed with great surprise that he was breathing. Then he realized that he was still in the water. _Under_ the water, to be precise.

He didn't know what had happened or how it was possible, but he was floating in what appeared to be an underwater cave that was illuminated by strategically placed globes filled with glowing corals and plants. He was also no longer cold, and, as his mind kept reminding him, _breathing_ despite being completely submerged.

Opening his mouth, Jace still half-expected to drown, but instead air bubbles escaped, along with his voice, sounding slightly distorted but otherwise normal as he asked shakily, "Hello? Anyone?"

"Oh, hi, you're awake!" Not having expected an answer, Jace whirled around, flailing wildly until he caught sight of two dark-haired heads peeking around the cave entrance, belonging to a boy about his age and a girl looking a few years younger. It had been the girl who'd spoken, but she kept behind the boy when they entered the cave, and Jace gaped, because as unlikely as it was, they both had _fish tails_!

The girl's tail was a deep burgundy, while the boy's was the color of the night sky, and they used them to swim closer with graceful movements. Strangely enough it looked entirely natural, making Jace wonder if his mind had reached its capacity for amazement and had decided to simply take everything in its stride, no matter how weird.

Finally remembering at least some of what his father had taught him, he quickly checked his belt and cursed under his breath when he found the sheath there empty. Focusing on this instead of everything else, he narrowed his eyes at the strangers and asked suspiciously, "Did you take my knife?"

" _That's_ your first question?" the fish boy shot back, rolling his eyes.

"Be nice, Alec," the girl admonished the boy beside her -- Alec, apparently -- before turning to Jace and saying in a much nicer tone, "Please excuse my brother, he's nicer than he looks."

"No, I'm not!" Alec protested immediately, obviously falling into a familiar pattern of behavior. Jace didn't have any siblings, having been raised pretty much apart from other people due to his father's paranoia, but he figured he had to be nice to know you never had to be alone.

Except Michael Wayland's warnings of outside danger had been proven all too valid, and Jace's hackles rose again immediately. Clenching his fists, he bit out, "Whatever. Just -- tell me what the hell is going on or let me leave!"

The siblings exchanged alarmed glances, and Alec raised both hands in a reassuring gesture. "Please, we know you must be confused, but you're safe here. My name's Alec Lightwood, and this is my sister Isabelle."

It was strange, but looking at him Jace did in fact feel reassured, although he knew rationally that he had no reason to trust these strange fish people. He regarded them more closely, trying to ignore their tails, which understandably had dominated his first impression of them.

The second-most obvious thing about them were strange black marks strewn over the pale skin of their human-looking upper bodies, almost like tattoos yet somehow different in a way Jace couldn't quite put his finger on. There was quite a bit of skin on display, too, both of them wearing tank tops. Alec's was a simple grey affair, but a bark of laughter escaped Jace when he realized that Isabelle's had an image of Disney's Little Mermaid on it.

"A mermaid?! Seriously?" he heard himself exclaim before he could think better of it. "Is that what you are? Mer... people?"

"You really ask the strangest questions," Alec marveled, sounding almost amused. However, he did deign to answer, "I guess that's what you land folks call us. There's a reason most of your cultures have stories about people living underwater - we've been around for longer than you have, although there's not very many of us left these days. Humans haven't exactly been kind to the oceans."

Jace suppressed the urge to apologize. Instead he asked after a moment's hesitation, "So why did you save me? Isn't that dangerous for you?"

"It is." This time it was Isabelle who replied, giving her brother a long sideways glance. "But Alec here was quite insistent."

"Iz, don't-" Alec tried to interrupt, but Isabelle shook her head decisively and talked over him. "You were as good as dead when he found you. He... he brought you back."

"What do you mean, _brought me back_?"

"See for yourself." In lieu of an explanation Isabelle pointed to Jace's stomach, which he only now registered was quite exposed, his black t-shirt reduced to mere shreds. Underneath, his skin was bearing a black mark, similar to the ones he'd noticed on Alec and Isabelle.

Obviously seeing the direction of Jace's gaze, Alec lifted his own shirt, and Jace drew a sharp breath. There, in pretty much the same spot, lay the exact twin of Jace's mark. With trembling fingers, Jace reached out and touched first his and then Alec's definitely-not-a-tattoo, feeling the merboy's abs contract when he grazed shy fingertips over the black lines. Otherwise Alec held completely still, hazel eyes serious as he let Jace explore.

"What did you do to me?" Jace's voice was barely more than a whisper. A part of him was scared to death because of all that had happened, all the things he didn't understand, yet almost more disquieting was the fact that his fear did not extend to Alec. Or Isabelle, really, but mostly Alec. As if he knew deep down that he could trust him -- with his life, with _everything_.

"I used rune magic to bind you to me and pull your soul from the brink of death back into your body," Alec explained somberly, voice quiet, a balm for the turmoil in Jace's mind. "And once we were connected, I was able to use more runes to heal you and give you the ability to survive down here."

With carefully telegraphed movements he pushed the remains of Jace's t-shirt higher, revealing several more of what were apparently _runes_. His fingers brushed over Jace's skin, leaving behind them trails of warmth. Jace shivered and had to force himself to keep listening, although the words didn't seem to matter. Somehow he knew Alec was trying to keep him calm, soothe his fears. "This is the rune we share, we call it a _parabatai_ bond. Without it, our magic wouldn't work on you. This one's for healing. This is breath. This is-"

"I get it," Jace interrupted rather abruptly, tearing himself away. For a moment hurt flashed in Alec's eyes, but the next instant he'd drawn back with a single sway of his tail, moving rather more elegantly than Jace's flailing scramble. His face turned into a stoic mask, although Jace didn't know how he could tell that that's what it was, except that he just did. Giving himself a mental shake, he focused back on the essential. "You keep saying 'bond' this, 'binding' that; that sounds like more than just something that makes those rune things work."

"Of course it's more," Isabelle forestalled her brother. "Alec didn't want to frighten you. With the parabatai bond he literally _brought you back from the dead_ , or as good as. In order to do this, he had to connect his very soul to yours. Forever. You have no idea what that means in our world!"

"Jeez, Iz, I thought we were trying not to scare him," Alec admonished, but he didn't correct her. "And how can he know? He didn't even know we existed before last night. Incidentally-" Alec redirected his attention back to Jace,"-what were you doing on the cliffs in the dark? They're dangerous even during the day. And why haven't we seen any search parties?"

Jace knew with utmost certainty that Alec was throwing him a lifeline, distracting him with simple questions from the overwhelming reality. Unfortunately Jace's answers were anything but simple, leaving him with a heavy, lead-like feeling in the pit of his stomach: "I was there because the only person who might have sent search parties after me-" although truthfully Jace doubted it, considering his father's insistence on keeping them apart from the world while he prepared Jace to fight some shadowy threat, "-had just been murdered. I was running from the men who killed my father when I fell."

"Oh no, how awful!" Isabelle exclaimed, dark eyes huge with pity. It set Jace's teeth on edge, and he was grateful to find no such thing in Alec's gaze, only sorrow and understanding. It was strange how this boy, who wasn't even human, somehow managed to look right into Jace's heart, making Jace wonder if that was another result of that _parabatai_ thing.

Which reminded him of a rather important question: "Umm, what exactly does it mean when you say our souls are connected forever? Until today I wasn't even sure souls existed. Am I supposed to stay here with you from now on?"

Isabelle opened her mouth, only to be stopped by Alec with a stern, "Iz. Leave us alone." When she pulled a face, he added in a softer tone, "Parabatai bonds are personal, you know that. Go tell mom and dad that our guest is awake and that I'm looking after him."

"Alright," Isabelle agreed grudgingly. Before swimming away, however, she turned to Jace and asked with a toss of her head, "Am I allowed to tell them your name, or is that personal, too?"

"Don't be a brat!" Alec swatted at her, but she evaded him easily, smirking. "Sometimes it's really obvious that you're still a child."

"Am not!"

Before the siblings could revert to petty squabbling, Jace quickly interrupted, "My name's Jonathan Christopher Wayland. You can call me Jace."

"Well, it's nice to meet you, Jace." Isabelle's kind smile grew teasing. "Welcome to the family!"

With that parting remark she whirled around and quickly swam out of the cave, leaving Jace gaping after her. He turned to Alec, intending to share a quip about little sisters, because he desperately needed a moment of normalcy, no matter how illusory it was. However, his words died on his lips, because Alec, who'd so far struck him as rather controlled, was looking positively bashful, ears red and teeth worrying his lower lip.

"What's the matter?" Jace asked, pointedly ignoring the part of him that found the sight rather endearing. When Alec quickly hid his emotions behind his usual serious facade, Jace shook his head firmly. "Don't tell me that it's nothing. Something your sister said struck a nerve -- and I think I deserve the truth. After all, we're bound together, aren't we?"

Much to his surprise, his words did the trick, rather more than he'd intended, because Alec stared at him intently, then nodded -- and gripped Jace's forearm. Jace wasn't used to physical contact that wasn't fight training with his father, and this simple gesture almost overwhelmed him. Alec's grasp was firm, warm, and felt like an anchor, one that Jace clung to. Their eyes met and held, which should only add to the tension stretching between them, yet Jace couldn't look away.

Nor did he want to, not even when Alec said in a low, serious voice, "That we are. We're parabatai now, Jace-" and no one had ever said Jace's name like this, like it was precious, "-and that means you're family. More than family, it's a bond only very few merpeople choose, because unlike blood or marriage the connection between parabatai is emotional, physical _and_ magical. We will literally live and die together."

"You mean..." Jace trailed off as his mind tried to digest Alec's explanation, torn between the urge to tear himself away from the merboy or cling to him more tightly.

The look in Alec's hazel eyes was kind. "Yes, when one of us dies, the other will, too." He squeezed Jace's arm reassuringly. "However, killing us will be harder now, because the bond offers some protection -- that's why I was able to bring you back."

"But I don't have to live here?" It wasn't that Jace was fundamentally opposed to the idea, discovering quite quickly that he wouldn't mind getting to know Alec better. Still, the idea that this immediate sense of familiarity was something forced upon him -- upon them both, really -- didn't sit well with his independent spirit. Still, he added quickly, "Not that I'm not grateful, it's just... a lot, you know."

Luckily Alec didn't seem offended. "I know it is. This isn't exactly how I expected things to turn out either, but at least I had some sort of choice in the matter."

It was funny, though; despite his words Jace was quite certain that the merboy hadn't considered it a choice, not when the alternative had been Jace's death. The thought made something deep inside Jace unfurl, something warm and pleased, and he found himself touching his left flank with is free hand, resting his palm over _their_ rune.

For some reason this made Alec flush and clear his throat. "Umm. Yeah. You absolutely don't have to live here. It's probably better if you don't, actually, although you will always have a home here." The _with me_ was left unspoken, but Jace blushed nonetheless. "We have friends on the surface, most of them non-humans -- what we call Downworlders and you'd call werewolves, warlocks, seelies, and vampires -- but some humans, too. You can live with them until we're old enough to... to..."

Alec's entire body language spoke of deep discomfort, his tail twitching nervously, his eyes refusing to meet Jace's. Not letting him pull away, Jace said with forced levity, "Oh, come on, you can't just drop the bombshell that all those creatures are real on me and then get all shy about the equivalent of merpeople drinking age or whatever we have to be old enough for."

A bark of laughter escaped Alec, and the thought hit Jace that his new -- savior? friend? bond mate? _paraba-whatever_ was really hot. He quickly dismissed it, only to be forcibly reminded only moments later, when Alec explained rather didactically, "Parabatai are usually older than we are, because the bond usually has a... a _physical_ component, drawing them together. Intimately, I mean."

In spite of his best efforts to sound casual, Alec's voice turned into a strangled mumble at the end, making his meaning abundantly clear. This time Jace did let go of him rather abruptly -- and promptly oversteered, sending him tumbling backwards through the water, something he'd almost forgotten. For a panicked second, during which he didn't know which way was up, his brain insisted that he was about to drown.

Instead he managed to right himself, coughing and raising both hands to stop Alec in his tracks when he wanted to swim to his side. Recovering enough of his composure to make some kind of sense, Jace cursed, "What the hell, Alec! Do you mean to say your weird mermagic will make us want to fuck each other?"

Alec was beet red, but he shook his head, appearing somewhat offended by Jace's choice of words. "It won't 'make us' do anything. But it _will_ intensify what we feel. For each other, I mean."

"But how could I feel anything for you? We don't even know each other," Jace protested. However, the words rang false in his own ears. Although they'd only just met and he didn't understand half of what was going on, there was no denying the connection between them, whether it was magically-induced or not. Stubbornly he added, "Also, I have no need for love. Love is dangerous, it only brings destruction."

Alec tilted his head, looking at Jace as if he could see right through his posturing. "Who taught you that? Your father?" When Jace only pressed his lips together in a thin line, the merboy's expression softened into a gentle tease. "And who said anything about love anyway?"

"You... Oh, shut up!" Jace couldn't stop himself from chuckling. For a moment the tension between them relaxed as they shared a smile. Never before had Jace felt this understood, this comfortable, with another person. Still, there was too much left to be discussed, yet Jace kept his voice carefully light when he asked, "So that's why you think it'd be better if I live on the surface, with those friends of yours? To keep us apart in case we can't keep our hands to ourselves? How positively Victorian!"

"It's not like there's a law about it or anything," Alec replied defensively. "But the rune wouldn't have taken if we weren't compatible. And would you really want to live under the sea? With Luke and Jocelyn you can have a normal human life -- or as good as, except that Luke's a werewolf. Jocelyn even has a daughter who's about Izzy's age and who goes to a regular mundane school and everything."

"But I could still come see you?" Jace wasn't quite sure why this felt absolutely vital, just as he wasn't sure at which point during their fraught conversation he'd drifted closer to Alec again. They weren't holding each other, but sometimes Alec's slowly swaying tail would brush against Jace's legs in their much less graceful efforts to keep him in place. As if in a trance Jace found himself reaching out, his hand hovering over the darkly glistening scales. Catching Alec's eyes, he asked quietly, "Can I touch it?"

"Of course." Alec's voice was equally low, creating the impression that they were in an intimate bubble. "Jace, you're my parabatai. I'm aware we haven't done things properly, but -- I'm yours, you know."

Jace flushed hotly, his instincts screaming at him to run while simultaneously there was no denying the pull he felt towards the merboy gazing at him with such frankness, as if his admission had been nothing out of the ordinary. Unable to meet Alec's darkening eyes, he ended up staring at his tail instead, the visible proof of the strange world Jace had literally fallen into. It was beautiful, irresistible, and before he could stop himself, Jace trailed his fingers over the cool scales.

Rationally he knew there was no great difference between touching Alec's tail and a fish, they were made from the same stuff. Yet there was no revulsion in his touch, only curiosity that turned into simmering excitement when Alec drew a sharp breath, the strong muscle quivering underneath Jace's palm. It made the blue-black expanse shimmer, reflecting the light from the illuminated globes like a hundred stars, turning what was basically an oversized fish tail into something otherworldly. Magical.

Jace looked up to discover Alec staring at him with pupils blown, and desire curled deep inside his stomach, hot and growing hotter. It was strange. The feeling was his own, of that he was sure, yet somehow it was also _Alec's_. Still touching the merboy's tail in what had at some point undeniably turned into a caress, Jace could hear his voice shake: "Alec, is this...?"

"Yes, that's the bond. _Parabatai._ " Jace was beginning to really like hearing Alec call him that, the way his voice curled around the word. He sounded as undone as Jace felt. "Jace, I never expected it to be like this."

"That makes two of us then." Jace huffed a laugh before adding solemnly, "So we'll just have to figure things out together."

"Together." Voice hoarse, Alec nodded before offering Jace his hand again. This time, when Jace clasped the merboy's arm, it felt like a promise. A vow. And before he could overthink, Jace had leaned in and pressed his lips against Alec's, swallowing the surprised gasp of his own name.

Jace had never been told why his father thought their seclusion necessary, only vague mentions of nebulous enemies that Jace needed to be ready to fight, but his upbringing hadn't exactly lent itself to romantic ventures. So while he'd been allowed into town on his own a few times once he'd turned 15, he'd only kissed two girls in his life, both stolen moments in the semidarkness of a pub he'd ventured into.

Neither one of those encounters had prepared him for Alec.

Setting aside the obvious fact that his current kissing partner wasn't human and that they were still floating underwater, every slide of the merboy's lips, every touch of their tongues, at first careful then increasingly bold, sent bolts of naked _want_ through Jace's entire body. Groaning, he clutched at Alec's shoulders with his free hand, the other still busy exploring the upper parts of his tail as well as the areas where scales seamlessly melted into warm, human skin.

The fact that at the same time curious fingers were finding their way underneath shirt, skimming up his back and leaving trails of fire in their wake, made everything all the more intense. Jace dimly realized that he'd begun to clumsily rub himself against Alec's firm center, wishing for the first time in a while for firm ground under his feet so he could gain better purchase.

Instead they were tilting over, still kissing hungrily, Alec's arms around Jace's waist stabilizing him on top of the merboy. It was easier this way, Alec's tail strong enough to balance them both until Jace could almost pretend that they were lying down. However, no amount of pretending could make him ignore the fact that, while his own dick had begun to strain against the zipper of his jeans, he could discover no similar reaction in Alec despite being pressed against him quite intimately.

But how could he, considering that Alec didn't have legs? Still, it was disconcerting enough for Jace to stop their kiss for long enough to blurt out, "I know you like this, I can feel it, but... do mermen not have dicks?"

Alright, so he could probably have phrased his question more politely, but in all fairness, most of Jace's blood wasn't currently occupying his brain. Alec would just have to deal, which he did by bursting into laughter, almost dislodging Jace from on top of him. After a moment Jace followed suite, not even minding when Alec subsequently put a little space between them, eyes still sparkling with amusement.

Whatever else their bond entailed, Jace was beginning to understand what Alec had meant earlier with their compatibility. Alec seemed to accept him completely, faults and all. The realization was too much, too soon, and Jace quickly pushed it aside for when it wouldn't overwhelm him so completely. Instead he focused back on Alec and shrugged with forced nonchalance. "How am I supposed to know? It's not like I had merpeople biology 101!"

"No, of course not." As always Alec appeared to read him easily, mirroring his light tone, although his already flushed cheeks turned even darker when he gestured towards the part of his tail that was approximately level with Jace's crotch. "We do have dicks, quite similar to human ones. Ours are just... hidden. Honestly, I always figured the way yours dangle about has to be uncomfortable!"

"Oh, it absolutely can be," Jace agreed with a laugh, pulling at his jeans in a not very subtle way that made Alec snort. Rolling his eyes at the merboy, Jace focused again on his original question: "So you have something like a hidden compartment in there, and you only take it out to, you know, do the deed?"

"More or less, yes. It's like this -- pouch? or something? Maybe it's easier if I show you." Clearing his throat Alec nodded quickly. Visibly squaring his shoulders he then grasped Jace's right hand and put it against an area that had first glance didn't look any different from the rest of his tail. However, when Jace carefully pressed down, he could feel that there was more give here than elsewhere he had touched. Still, if Alec hadn't guided his fingers, he could easily have overlooked the slight overlap in scales, softer and more flexible as his fingertips suddenly slipped inside. Alec hissed, but when Jace made to pull back he shook his head. "It doesn't hurt. It's just -- no one's ever touched me there."

Holding his breath, Jace let Alec direct him along the slit, completely enthralled, especially when, despite the initial comparison to a vagina that had popped into Jace's head, he could feel something harden and rise to meet his carefully questing fingers. Dropping his hand abruptly, Alec flinched back, blushing hotly. "Sorry, I didn't mean..."

"Don't be," Jace shushed him firmly, although he felt hot all over. "If what you told me is true-" which he didn't really doubt anymore, "-I'll get to see it sooner or later anyway. And you already felt mine, after all."

Alec chuckled ruefully. "True. But maybe not just yet. I think you've had quite enough shocks for one day. And, truthfully, so have I."

The reminder of the enormity of Alec's selfless decision to save Jace struck him once again, and all he could do was nod dumbly. "I know this sounds stupidly inadequate, but -- thank you."

"Jace, there's no need for thanks between us," Alec assured him simply. "I might not have planned for you, but I'm glad it was me who found you. Even if you decide to never come back."

"Don't be stupid." Jace blinked back sudden tears, glad Alec probably couldn't tell because they were already submerged in water. "Of course I'm coming back. You're my family now, aren't you? My -- parabatai."

***

Jace did, in fact, return to the sea and to Alec regularly.

He enjoyed living with the Fray-Garroway family, basically gaining a sister in Clary and surrogate parents in Jocelyn and Luke. The latter was glad to continue his combat training, not just the regular, human styles Jace's father had taught him, but also taking him to meet various Downworlders. Jace definitely had fun training with Luke's wolf pack or the vampire clan Clary's boyfriend Simon belonged to, and he also made the most of his first mundane highschool experience.

As time passed, Jace realized with quiet surprise that instead of being a lonely orphan he basically had not just one but _two_ adopted families, the Lightwoods always happy to welcome him. In the end it was Alec who stuck by his side when two years later, just before Jace's highschool graduation, the man he'd always thought was his father returned.

Michael Wayland revealed himself to be none other than Valentine Morgenstern, a famed Downworlder hunter, and for a while even people Jace had considered close friends looked at him with suspicion. Never Alec, though.

In an act of defiance against all who dared doubt Jace's allegiance, Alec decided that this was the moment for them to formalize their parabatai bond. By undergoing the public challenge and ceremony they declared to anyone with the slightest knowledge of mer culture that Alec would always be on Jace's side, that nothing would ever tear them apart.

Floating in a circle of glowing corals, feeling Alec's night-blue tail twine around his legs while they clasped hands and repeated the sacred words of an oath they'd previously skipped for obvious reasons, Jace looked at his parabatai, the one who'd given him life in more ways than one, and knew that he'd never regret binding his soul to the young merman. Even now Alec's very being shone with his unwavering love for Jace, causing the rune they shared to pulse warmly.

In breach of mer tradition Jace pulled his parabatai closer and pressed a firm kiss to his surprised smile. He might not have chosen this bond, but he would always be grateful that Alec did.

***


End file.
